1. Field of the Invention
The present invention relates to a tracking method for use in recording data on and reproducing data from a high-density optical disc having lands and grooves and a tracking apparatus adopting the same, and more particularly, to a method for accurately tracking servo-controlling both a shallow groove type optical disc and a deep groove type optical disc which are loaded in a recording and/or reproducing system and an apparatus adopting the same.
2. Description of the Related Art
Recently, in the optical disc technical field, optical discs are being developed and vary from a low-density laser disc (LD) and compact disc (CD) to a high-density digital versatile disc (DVD). A currently developed DVD enlarges the numerical aperture (NA) of an objective lens in an optical pickup and uses a short wavelength laser, and thus largely enhances a recording density when compared with an existing CD. As an example, a digital versatile disc-random access memory (DVD-RAM) having a recording capacity of 2.6 GB was developed using a laser beam having a wavelength of 650 nm. Recently, a DVD-RAM of 4.7 GB has been developed by further narrowing a track pitch thereof and further shortening the length of a pit which is used for actually recording information.
Generally, an optical disc having a recordable and reproducible land/groove has a periodic arrangement of lands and grooves of the same pitch. Here, a recording and/or reproduction system records data on and reproduces the data from each land and groove of a loaded optical disc. FIG. 1 shows the structure of lands and grooves on a known shallow groove type optical disc. The shallow groove type optical disc is defined as an optical disc on the substrate of which grooves of .lambda./8+L n through .lambda./4+L n in depth are formed, in which .lambda. is a laser wavelength of an optical pickup and n is a refractive index of the substrate of the optical disc. As shown in FIG. 1, the optical disc has a track pitch 3 of 0.74 .mu.m defined as a width ranging from the center of a land 1 to that of a groove 2 and a groove depth 4 of .lambda./6.5+L n where laser incident light 5 having a wavelength (.lambda.) of 650 nm is used for the optical disc.
Meanwhile, FIG. 2 shows the structure of lands and grooves on a known deep groove type optical disc for enhancing a recording density in comparison with the shallow groove type optical disc shown in FIG. 1. The deep groove type optical disc is defined as an optical disc on the substrate of which grooves of .lambda./4+L n through .lambda./2+L n in depth are formed, in which .lambda. is a laser wavelength of an optical pickup and n is a refractive index of the substrate of the optical disc. As shown in FIG. 2, the optical disc has a shorter track pitch 13 of 0.58 .mu.m (the width from the center of a land 11 to that of a groove 12) and a shorter pit than those of FIG. 1 in which laser incident light 5 of 630 nm, shorter than that of FIG. 1, is used for the optical disc. In this case, cross-talk increases due to interference from signals recorded on neighboring tracks during reproduction of data, and more influences are given to neighboring tracks during recording and erasing data. To solve these problems, the optical disc of FIG. 2 has a groove depth 14 of .lambda./3+L n deeper than that of FIG. 1 to thereby minimize the effects due to the signal interference from the neighboring tracks.
Meanwhile, a tracking error signal (TES) should be obtained from an optical disc, in order to servo-control an optical pickup so that the beam spot from the optical pickup performs an exact tracking over the center line of a target track on the optical disc, during recording and reproducing data. In a push-pull method chiefly adopted for this purpose, two-division-photodiodes (2D-PD) or four-division-photodiodes (4D-PD) which are arranged symmetrically left and right with respect to the center line of a track detect the strength of the light reflected and diffracted from the optical disc, and a left-right light strength difference of signals detected with respect to the center line of the track is obtained as a tracking error signal. The tracking error signal of the push-pull method is called a push pull signal (PPS). A tracking servo portion complementarily drives an actuator for driving an objective lens or a rough-movement motor for driving the entire optical pickup portion, using the obtained tracking error signal, to thereby servo-control the optical pickup so that the beam spot of the optical pickup performs an accurate tracking over the center line of the target track.
However, the tracking error signal detected from the above-described deep groove type optical disc is reversed in phase (polarity) in comparison with that detected from the shallow groove type optical disc. As a result, when a recording and/or reproduction system for the shallow groove type optical disc performs a tracking servo control over the deep groove type optical disc, an error occurs in the tracking error signal. Thus, an accurate tracking servo control cannot be performed.